The present invention relates to a method for splicing a first length or web of film material to a second web of film material. It also relates to a device for carrying out the said method comprising a roll for unwinding a first web of film material to be spliced, a roll for winding film material to be spliced and a splicing table subjected to vacuum and having a cutting groove over which the web of film to be wound or unwound can pass, together with means for applying an adhesive splicing tape.
The splicing of two extremely thin films is a difficult operation involving problems not only in making the actual splice, but also in ensuring that the splice obtained is sufficiently reliable and does not in any way alter the behavior of the thin film material during subsequent processing (application of metallization to the film surface, or even reading and/or writing of information on said film after application of a magnetic material coating thereto) or during winding or unwinding. It is in fact an extremely difficult operation to accurately apply a narrow tape of adhesive film simultaneously onto two prepared end portions of film strip, principally as as a result of the significant electrostatic forces that exist between the two end portions of the static-charged film, prior to bringing the adhesive tape into bonding contact with said film, such electrostatic charges almost always having the effect of causing one of the three elements involved in the splicing operation to move with respect to the two others prior to bonding contact being able to be achieved. Moreover, splices formed in a web of extremely thin film using a narrow strip of splicing tape have to date proved to be totally unsuccessful in withstanding repeated folding and tractional forces to which they may be subject, not as a result of a lack of strength of the bonded surface but rather through the effect of shearing forces that are exercised by two lengths of spliced film in which the ends are in a touching or to all intents and purposes a touching or butt relationship.
A further significant disadvantage of splices provided in thin films that take the form of a butt joint to which a narrow band of splicing tape has been applied results from the sudden shock which is inevitably produced by the excess thickness at the point of splicing when the film passes between guide or drive rolls or even in front of a read and/or write head in the case where the film is used as an information carrier by application of a magnetic material coating thereto, or during other suchlike operations on the tape. Similarly, metallization operations which are currently carried out on films that have been spliced exhibit visual discontinuities and other manifestations in the spliced area.
One object of the present invention consists in providing a method and a device for splicing two lengths of thin film in which accurate joining of the two portions of film is facilitated and partly automated without the participants in the splice being able to move under the effects of static electricity.
A further object is to provide a splice between two portions of thin film which during use is not only as strong when subject to tractional forces as the unspliced film but which also is as strong, when subject to alternating bending forces and to general stresses, as the original film whereby if the film does break, it does not break at the splice but rather at another point on the film.
A further object is to obtain a splice in two lengths of extremely thin film where the splice itself is as thin as possible. To achieve such a thin splice, it should be possible to employ a very thin adhesive splicing tape which, after application to said thin film, is barely thicker than the spliced film, bearing in mind that splices in thin film are currently provided using splicing tape which, in the case of very thin films, is some twenty times thicker than the film itself, in order to obtain sufficient rigidity and mechanical strength from the narrow strip of splicing tape.